(a) A student studied the structure of a mammalian heart. The student took a photograph of the left side of a dissected heart as shown in Fig. 6.1. Identify two features of the left side of the heart visible in Fig. 6.1 and explain how each feature is adapted to the function of the heart. (b) Cardiac muscle is described as myogenic. This means the electrical activity controlling the rhythm of a regular heartbeat begins within the muscle tissue of the heart. Describe how electrical activity within the heart controls each heartbeat. (c) Tissue fluid is formed from blood plasma as it flows through capillaries. Fig. 6.2 is a diagram of a capillary and some adjacent tissue cells in a capillary network. (d) Measles is a common disease caused by a virus. Vaccination to prevent the disease has been very successful.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2025). The mark or mark type is shown in brackets.

1. [1] any two of these pairs, feature and explanation
2. [1] thick wall of (left) ventricle ; R if right
3. [1] pumps blood at high pressure to, reach (all of) systemic circulation / overcome resistance in systemic circulation / over a long distance / AW;
4. [1] A if thick wall unqualified A generate high force
5. [1] R 'withstands high pressure'
6. [1] thin wall of (left) atrium ;
7. [1] pumps blood at low pressure, into ventricle / over a short distance ;
8. [1] either
9. [1] (named) valves ; R tricuspid / pulmonary
10. [1] prevent, backflow of blood / maintains one-way flow of blood (through heart) ;
11. [1] ecf if right atrioventricular / tricuspid
12. [1] or
13. [1] (left) atrioventricular / mitral / bicuspid, valve; R right
14. [1] prevents, backflow of blood / blood flowing from ventricle to atrium ;
15. [1] A maintains one-way flow of blood (through heart)
16. [1] or
17. [1] (left) semi-lunar, valve;
18. [1] prevents, backflow of blood / blood flowing from, aorta / artery, to ventricle ;
19. [1] A maintains one-way flow of blood (through heart)
20. [1] chordae tendinae / tendons / tendinous cords / AW ; I ligaments
21. [1] hold the valve in position, during systole / when ventricle contracts / AW ;
22. [1] A prevents blowback / turning inside out
23. [1] I high tensile strength unqualified
24. [1] AVP ;; e.g papillary muscle ;
25. [1] contracts to hold, tendons / valve, when heart contracts / during systole ; ora
26. [1] any four from:
27. [1] if AVN used penalise once and then use ECF
28. [1] sinoatrial node releases, waves of excitation / waves of depolarisation / (electrical) impulses / action potential(s); AW
29. [1] impulses / AW, stimulate, (both) atria to contract / atrial systole ;
30. [1] impulses / AW, prevented from reaching ventricles by, fibrous ring / non-conducting tissue / insulating tissue / (between atria and ventricles) ; A annulus fibrosus
31. [1] atrioventricular node, delays impulse (by 0.1 s) ;
32. [1] atrioventricular node, sends impulse to, Purkyne tissue (in septum); A bundle of His
33. [1] allow ecf for abbreviating AVN
34. [1] Purkyne tissue conducts impulse to, base of ventricles / apex of heart, so they contract ;
35. [1] any two from: if transport is used in MP2 to MP8, penalise once and mark to a max of 1 for those MPs
36. [1] provides, aqueous/watery, (external) environment / surroundings, for cells
37. [1] to maintain correct water potential
38. [1] to prevent, cell dehydration / excessive water loss from cells ;
39. [1] idea that provides medium for exchange of substances
40. [1] supply of oxygen / oxygen diffuses from blood into tissue fluid ;
41. [1] removal of carbon dioxide / carbon dioxide diffuses from tissue fluid into blood ;
42. [1] A exchange of (respiratory) gases as alternative to MP2 and MP3
43. [1] supply of named nutrient e.g. glucose, amino acids, (named) ion(s);
44. [1] removal of, metabolic / toxic, waste or urea ;
45. [1] location / movement, of (tissue) macrophages / neutrophils / phagocytes (for defence) ; I white blood cell
46. [1] allows movement of / medium for passage of, (named) cell signalling molecules / hormones / ligands ;
47. [1] A ref. to cells signalling nearby cells / paracrine signalling
48. [1] AVP; e.g. contributes to formation of lymph / contains antibodies
49. [1] e.g. allows movement of lymphocytes into lymph
50. [1] any three from:
51. [1] (at arteriole end of capillary) high, hydrostatic / blood, pressure ;
52. [1] (ultra)filtration / described ;
53. [1] e.g. fluid / plasma/water and solutes, forced / comes, out of, capillaries / blood
54. [1] glucose / amino acids / ions, leave blood R if stated, red blood cells / platelets, leave
55. [1] or
56. [1] (large) plasma proteins remain in blood ;
57. [1] through, fenestrations / fenestrae / endothelial pores
58. [1] or
59. [1] through, pores / gaps / spaces, in, capillary wall / endothelium / between cells ;
60. [1] AVP; e.g. ref. to hydrostatic pressure gradient
61. [1] hydrostatic pressure of blood is greater than hydrostatic pressure of tissue fluid
62. [1] I pathogen A epitope for antigen
63. [1] any two from:
64. [1] some (T-lymphocyte) have (T-cell) receptors, specific / complementary, to a particular antigen ; ora
65. [1] antigen (in vaccine) binds to these T-lymphocytes ;
66. [1] idea that only these T-lymphocytes are, activated / stimulated / selected ; I respond
67. [1] AVP; e.g. some T-lymphocytes do not become exposed to limited quantity of antigen in vaccine
68. [1] max four if no correct ref. within response to, memory cells / immunological memory
69. [1] any five from:
70. [1] context of primary immune response
71. [1] antigen presentation by macrophages;
72. [1] (T-/B-) lymphocyte, binding / recognition / clonal selection / activation / described in terms of receptor ;
73. [1] clonal expansion / cell divides by mitosis many times (to produce a clone) / AW ;
74. [1] cytokines released by T-helper, cells / lymphocytes ;
75. [1] (stimulate) formation of memory, (T- / B-) lymphocytes / cells ;
76. [1] (memory cells) remain in, circulation / body, for a long time / AW ; A remain in lymph nodes
77. [1] or
78. [1] memory cells are long-lived ;
79. [1] context of secondary immune response
80. [1] large numbers of (specific), memory cells / lymphocytes ; I more memory cells
81. [1] A memory cells have a higher chance of encountering antigen